This invention relates to subsea completions incorporating isolation valves for well containment and other purposes.
Subsea Christmas tree tubing hangers typically have wireline plugs installed in the production bore as a barrier to enable removal of the BOP. The setting and sealing of the wireline plugs is both unreliable and time-consuming, especially at increased well depths. Additionally, it would be advantageous to avoid having to pull the wireline plugs through the riser, as this necessitates an expensive lower riser package/emergency disconnect package trip.
European Patent No 0845577 discloses a wellhead assembly having an in-line tree received within a wellhead housing and forming a production bore including a pair of remotely actuated ball valves. This eliminates the need to set wireline plugs in the production bore and has further operational advantages. In particular, it allows the tree and, tubing hanger to be run without disconnecting the BOP, and allows removal of a separate horizontal tree connected to the wellhead, without use of a BOP. However the valves and their actuators take up a relatively large amount of space within the wellhead. Consequently the wellhead and the tubing hanger received in it must also been made relatively large in diameter. The ball valves used also have relatively limited wireline shearing capabilities.
European Patent No. 0624711 discloses a tubular member in which is landed a valve assembly having a gate valve. Actuators positioned externally of the tubular member include actuating stems in engagement with opposite sides of the valve gate.
The present invention provides a subsea completion having an in-line Christmas tree received within a wellhead, the in-line Christmas tree including a valve closure element; a valve actuator coupling being operatively engaged with the valve closure element and extending through walls of the in-line Christmas tree and wellhead, and a jumper module that can be secured and sealed to the wellhead and connected to an independent flow control package. Relatively bulky valve actuator mechanisms may therefore be mounted externally of the wellhead, with only the relatively small and unobtrusive actuator coupling extending into the wellhead and tree interiors. The size of the tree, tubing hanger and wellhead may thus be kept reasonably small. The actuator coupling can be operated either manually, or hydraulically with optional manual override. In both cases the manual operation may be performed by an ROV. The introduction of valves contained within the wellhead obviates the use of wireline plugs, thereby reducing trip times, providing remote operation without wireline trips and increasing system reliability.
If required, the valve closure element can also be used to shear wireline, coiled tubing or the like passing through the in-line Christmas tree, in addition to sealing the bore in which the valve closure element is situated. The valve closure element is preferably a valve gate, which provides excellent shearing capability and is the preferred oil industry valve closure element for a subsea system.
The actuator coupling may be a rising stem type actuator shaft attached to the valve gate, or alternatively a longitudinally fixed threaded shaft engaged with a lift nut in the valve gate. Preferably however, the actuator coupling comprises a pair of push rods each extending through the wellhead wall and arranged to press on opposed edges of the valve gate to move it between open and closed positions. On withdrawal of the push rods there is no interconnection between the in-line tree and its valve actuators. The in-line tree and valve actuators therefore may be installed or removed independently of each other.
Providing the valve closure element as an integral part of the completion allows the completion to be rapidly isolated without the need to run wireline plugs. There is then no need to run a lower riser package and emergency disconnect package on a completions riser that would otherwise be required to control intervention to the well and to remove wireline plugs prior to flowing the well.
Integration of valve closure elements or closure valves within both the production and annulus bores of the completion will ensure rapid and reliable sealing.
There are further operational benefits from this invention. The valve closure element will allow the wellhead to be easily sealed after installation of the completion components using a drilling vessel. This can allow drilling and suspension of the well at an early stage, so that at a later date a more basic installation vessel can recommence the installation of the subsea Christmas tree system. This will avoid using the drilling vessel for a lengthy Christmas tree installation and will therefore reduce costs.
Additional operational flexibility can be obtained by using the jumper module secured and sealed to the wellhead in place of an integrated flow control module comprising a subsea Christmas tree. This jumper module is then connected to an independent flow control package which contains the necessary flow control equipment.
The wellhead may be of unitary construction, or may comprise a separate tubing spool secured to a wellhead lower part and containing the in-line tree.
Further preferred features are described below in connection with illustrative embodiments of the invention shown in the drawings.